The present invention relates to subterranean treatment fluids and associated methods. More specifically, in certain embodiments, the present invention relates to cement compositions that comprise a particulate elastomer having a specific gravity of at least about 1.05 and associated methods.
Cement compositions are one type of subterranean treatment fluid that may be used in a variety of subterranean applications. For example, in subterranean well construction, a pipe string (e.g., casing, liners, expandable tubulars, etc.) may be run into a well bore and cemented in place. The process of cementing the pipe string in place is commonly referred to as “primary cementing.” In a typical primary cementing method, a cement composition may be pumped into an annulus between the walls of the well bore and the exterior surface of the pipe string disposed therein. The cement composition sets in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement (i.e., a cement sheath) that may support and position the pipe string in the well bore and may bond the exterior surface of the pipe string to the subterranean formation. Among other things, the cement sheath surrounding the pipe string functions to prevent the migration of fluids in the annulus, as well as protecting the pipe string from corrosion. Cement compositions also may be used in remedial cementing methods, for example, to seal cracks or holes in pipe strings or cement sheaths, to seal highly permeable formation zones or fractures, to place a cement plug, and the like. Cement compositions also may be used in surface applications, for example, construction cementing.
Once set, the cement sheath may be subjected to a variety of cyclic, shear, tensile, impact, flexural, and/or compressive stresses that may lead to failure of the cement sheath, resulting, for example, in fractures, cracks, and/or debonding of the cement sheath from the pipe string and/or the formation. This may lead to undesirable consequences such as lost production, environmental pollution, hazardous rig operations resulting from unexpected fluid flow from the formation caused by the loss of zonal isolation, and/or hazardous production operations. Furthermore, failure of the cement sheath also may be caused by forces exerted by shifts in subterranean formations surrounding the well bore, cement erosion, and repeated impacts from the drill bit and the drill pipe.
To counteract these problems, various additives may be included in the cement composition to enable the cement composition to withstand cyclic changes in imposed stresses. For example, hydrocarbon-based elastomers (e.g., styrene-butadiene random and block copolymers, acrylonitrile-butadiene, and acrylonitrile-styrene-butadiene elastomers) have been included in cement compositions to modify the mechanical and expansion properties of the cement composition. Generally, such materials are used in the particulate form. As used herein, the term “particulate” refers to materials in solid state having a well-defined physical shape as well as those with irregular geometries, including any particulates elastomers having the physical shape of platelets, shavings, fibers, flakes, ribbons, rods, strips, spheroids, hollow beads, toroids, pellets, tablets, or any other physical shape. Among other things, the particulate elastomers may function to control shrinkage cracking in the early stages of the cement setting process, and also may provide resiliency, ductility, expansion, and toughness to the set cement composition (e.g., the cement sheath) so that it resists and seals cracking or fracturing.
The use of particulate elastomers in cement compositions, however, may be problematic. For example, particulate elastomers used heretofore generally have a density equal to or less than water. Accordingly, these particulate elastomers may be particularly suited for use in lower-density cement compositions. These low-density particulate elastomers have also been used in higher-density cement compositions (e.g., greater than about 15 pounds per gallon), as no suitable higher-density particulate elastomers have been available. However, when used in the higher-density cement compositions, heavyweight additives may need to be used to compensate for the low-density particulate elastomers. The concentration of the heavyweight additives that may be needed to compensate for the low-density particulate elastomers, however, may undesirably affect certain properties of the cement compositions, such as its mixability and rheology.